Surface morphological evolution and microhardness change of Cr12MoV steel by pulsed laser polishing

Abstract

Laser polishing is gaining more and more attention because of its environmental friendliness and ability to process complex surfaces. It is considered as one of the technologies to replace traditional methods in the mold industry. In this work, the variation pattern of surface roughness with single pulse energy density and light-out overlap rate during nanosecond pulsed laser polishing of Cr12MoV steel was investigated. The surface roughness increased and then decreased with increasing single-pulse energy density and beam overlap rate, respectively. The lowest surface roughness was found to be 0.50 μm, which is a decrease of 79.34 % compared to the untreated sample. The effect of each parameter on the surface morphology during the laser polishing process is explained. There is minimal austenitization on the surface of the sample after laser polishing. The second phase of the remelting layer disappeared. The microhardness of the remelting layer increased by 36.17 % because the grain size was reduced by 30.65 %. This work further explains the mechanism transformation threshold for pulsed laser polishing of steel. With 95 % beam overlap, the melting and gasification energy density thresholds for Cr12MoV steel are respectively 1.269 J/cm2 and 2.937 J/cm2. The beam overlap rate of 95.5 % is the critical condition for continuous melt movement. It provides a new idea for the mechanism judgment of pulsed laser polishing.